U.S. patent application number 10/171512 was filed with the patent office on 2003-01-23 for catalytic coating of structured heat exchanger plates.
Invention is credited to Nowak, Dagmar, Roeser, Thomas, Schmidt, Michael, Zur Megede, Detlef.
Application Number | 20030014865 10/171512 |
Document ID | / |
Family ID | 7688425 |
Filed Date | 2003-01-23 |
United States Patent
Application |
20030014865 |
Kind Code |
A1 |
Nowak, Dagmar ; et
al. |
January 23, 2003 |
Catalytic coating of structured heat exchanger plates
Abstract
A process for producing a coated, structured heat exchanger
plate for a reactor in a fuel cell system comprises application of
a catalytic component in at least one layer by means of pad
printing, exclusively in the recesses and/or the flanks of the heat
exchanger plate.
Inventors: |
Nowak, Dagmar; (Winnenden,
DE) ; Roeser, Thomas; (Dettingen/Teck, DE) ;
Schmidt, Michael; (Nuremberg, DE) ; Zur Megede,
Detlef; (Kirchheim/Teck, DE) |
Correspondence
Address: |
CROWELL & MORING LLP
INTELLECTUAL PROPERTY GROUP
P.O. BOX 14300
WASHINGTON
DC
20044-4300
US
|
Family ID: |
7688425 |
Appl. No.: |
10/171512 |
Filed: |
June 14, 2002 |
Current U.S.
Class: |
29/890.03 |
Current CPC
Class: |
B01J 2219/2479 20130101;
Y10T 29/4935 20150115; B01J 2219/2461 20130101; B01J 19/249
20130101; Y02E 60/50 20130101; H01M 8/0631 20130101; B01J 2219/2459
20130101; B01J 2219/2458 20130101; H01M 8/04074 20130101; F28F
3/046 20130101; Y02P 70/50 20151101; F28D 9/005 20130101; B05D 1/28
20130101; B01J 35/04 20130101 |
Class at
Publication: |
29/890.03 |
International
Class: |
B21D 053/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 16, 2001 |
DE |
DE 101 29 099.3 |
Claims
What is claimed is:
1. A process for producing a coated, structured heat exchanger
plate for a reactor in a fuel cell system, comprising: applying a
catalytic component continuously or discontinuously in at least one
layer, by means of pad printing, exclusively to at least one of
recesses and flanks of the heat exchanger plate.
2. The process according to claim 1, wherein: said catalytic
component is applied in at least two stages; and each stage is in a
different zone of the heat exchanger plate.
3. The process according to claim 1, wherein said catalytic
component contains at least one of a catalytically active material
component and a hydrophobic material component.
4. The process according to claim 3, wherein said catalytically
active material component is in supported form.
5. The process according to claim 3, wherein said catalytically
active material component contains at least one of a ceramic binder
and a polymeric binder.
6. The process according to claim 3, wherein at least one of
composition and concentration of said catalytically active material
component is varied over the length of the heat exchanger
plate.
7. The process according to claim 1, wherein: the process is
carried out at room temperature; and the printing medium and
coating material are not heated.
8. The process according to claim 7, further comprising a drying
step at a temperature between 100.degree. C. to 200.degree. C.,
inclusive, subsequent to said applying by means of pad
printing.
9. The process according to claim 7, wherein the heat exchanger
plate is heated while the catalytic component is being applied.
10. The process according to claim 8, further comprising a final
step of calcining at a temperature of approximately 500.degree.
C.
11. A process for producing a coated, structured heat exchanger
plate for a fuel cell reactor, comprising: applying at least one
layer of a catalytic component to at least one region of the heat
exchanger plate with a printing medium, wherein said catalytic
component is applied exclusively to at least one location selected
from the group consisting of: the heat exchanger plate recesses and
the heat exchanger plate flanks
12. The process according to claim 11, wherein said at least one
layer comprises at least two different catalysts.
13. The process according to claim 11, wherein said at least one
layer comprises a thickness of 5 to 50 .mu.m.
14. The process according to claim 11, wherein a gradient is
created by applying said catalytic component in at least two
different thicknesses.
15. The process according to claim 11, wherein said catalytic
component is a catalytically active material.
16. The process according to claim 15, wherein said catalytically
active material further comprises a thermal stabilizing agent.
17. The process according to claim 11, wherein said catalytic
component is a hydrophobic material.
18. The process according to claim 11, wherein said catalytic
component is a combination of a catalytically active material and a
hydrophobic material.
19. A device for coating a heat exchanger plate for a fuel cell
reactor, said heat exchanger having a three dimensional structured
contour including a plurality of recesses and flanks, said device
comprising: a printing pad, wherein said printing pad is made of a
smooth elastic material which is deformable to match the three
dimensional contour of the heat exchanger plate by being pressed
thereon; whereby a catalytic component applied on said printing pad
is deposited in the form of at least one layer on at least one of
the flanks and recesses of said three dimensional contour.
Description
[0001] This application claims the priority of German Patent
Document DE 101 29 099.3, filed Jun. 16, 2001, the disclosure of
which is expressly incorporated by reference herein.
BACKGROUND AND SUMMARY OF THE INVENTION
[0002] The invention relates to a process for producing a coated,
structured heat exchanger plate for a reactor in a fuel cell
system.
[0003] A process for applying electrode layers to a strip form
polymer electrolyte membrane for fuel cells is described in DE 199
10 773 A1. The electrode layers are continuously printed in the
desired pattern on the front and rear surfaces of the membrane
using an ink which contains an electrocatalyst. The electrode
layers which have been printed on the membrane are dried at
elevated temperature immediately after the printing operation. The
printing is carried out so as to maintain a positionally accurate
arrangement of the patterns of the electrode layers on front and
rear surfaces. The printing operation in this case is carried out
on a planar surface. In addition, the printing may be accomplished
by stencil printing, offset printing or screen printing, or be
carried out by means of pad printing.
[0004] Hitherto, structured heat exchanger plates have usually been
spray-coated, wash-coated or dip-coated in order for coatings to be
applied. However, spray-coating causes a loss of coating material
of up to 50% as a result of overspray. During the production of
welded, structured heat exchangers comprising spray-coated plates
which are coated over their entire surface, layer flaking occurs at
the contact points. If welded reactors of this type are wash-coated
or dip-coated, deposits form at the contact points and these
deposits likewise flake off readily when thermal stresses occur.
The resulting drawback in the form of discharged catalyst dust
leads not only to higher costs on account of the loss of catalyst
but also to disruptions to the entire fuel cell system. The
disurptions occur through the presence of impurities in the
pipeline systems which results in, inter alia, the filters becoming
blocked, ignition in undesirable areas of the system, and damage to
valves.
[0005] Therefore, it is an object of the invention to provide an
inexpensive process for coating a structured heat exchanger plate
for a reactor, in which discharge of catalyst as a result of
mechanical and/or thermal stress during production or when a fuel
cell system is operating is virtually avoided.
[0006] To achieve this object, the present invention provides a
process for producing a coated, structured heat exchanger plate for
a reactor in a fuel cell system in which a catalytic component is
applied continuously or discontinuously in at least one layer, by
means of pad printing, exclusively in the recesses and the flanks
of the heat exchanger plate.
[0007] Further advantages of the process according to the invention
result from the high reliability of the process and the resulting
high-quality product, and the fact that process steps are
eliminated. Moreover, this process is far more environmentally
friendly than the other processes mentioned, since this process
does not cause any spray mist or overspray which has to be
discharged and disposed of.
[0008] The invention is illustrated diagrammatically and by way of
example in the drawings and is explained in more detail below with
reference to the drawings.
BRIEF DESCRIPTION OF THE INVENTION
[0009] FIG. 1 shows a plan view of a corrugated plate;
[0010] FIG. 2 shows the overlap of the corrugations when the plates
are stacked and resulting contact points;
[0011] FIG. 3 shows a cross section through two welded, corrugated
plates; and
[0012] FIG. 4 shows an outline sketch for the pad printing of a
corrugated plate.
DETAILED DESCRIPTION OF THE INVENTION
[0013] In the process according to the invention for the production
of a coated, structured heat exchanger plate 1 for a reactor in a
fuel cell system, a catalytic component is applied continuously or
discontinuously in at least one layer, by means of pad printing,
exclusively in the recesses 2 and/or flanks 3 of the heat exchanger
plate 1. (See FIG. 4.) Therefore, no coating is applied to the
surface of the raised parts 4 of the heat exchanger plate. When the
individual heat exchanger plates are joined to form reactors, which
are only peripherally welded, therefore, the contact surfaces 5 or
contact points are not covered with the catalytic component. This
targeted coating minimizes the release or flaking of the catalyst
that leads to catalyst being discharged as a result of mechanical
and/or thermal stress.
[0014] The coating of these structured plates is carried out by
means of pad printing. Pad printing is an indirect printing
process, i.e. a plate, which is known as an engraving, serves as
the original, on which the image to be printed is present in the
form of a recess. What is known as a printing paste or printing
liquid is spread over the engraving by means of a doctor blade and
is then drawn off again. The printing paste or printing liquid
remains in place in the recesses in the engraving. A smooth,
elastic stamp, known as the pad 6, preferably produced from
silicone rubber, by being pressed on, picks up some of this coating
material from the recesses and transfers this material to the
object 1 which is to be coated. The elasticity of the silicone
rubber means that the pad 6, as illustrated in FIG. 4, can match
the object which is to be printed when it is releasing the printing
paste or printing liquid. This allows the printing of non-planar,
structured plates, in which advantageously only the recesses 2
and/or flanks 3 but not the raised surfaces 4 of the structured
plate 1 are to be printed.
[0015] The coating of the heat exchanger plate with the catalytic
component can take place by one or more imprints covering the
entire area of the plate. However, the coating may also be effected
by coating the heat exchanger plates in zones. Multiple printing
allows the individual layers to be functionalized, so that, for
example, a different catalyst is applied to the reactor inlet from
that applied to the reactor outlet. Alternatively, or in addition,
the quantity of catalyst can be varied over the length of the
plate, in order to set up a gradient. In both the above cases, this
procedure is used to selectively control conversions and reactions
within the reactor.
[0016] If it were desired to carry out this procedure by means of
spray-coating, complex masking of the respective zones would be
necessary. This would make the process unnecessarily expensive and
relatively complex to realize, in addition to the overspray effect.
Zoned coating cannot be achieved by means of wash-coating or
dip-coating, so at best it is possible to apply a gradient in
coating height using these methods. The above process can be
carried out either discontinuously or continuously, with the plate
or plate strip being stopped briefly during the printing operation,
printed and then moved onward by a defined repetition length under
the control of sensors. The layer thicknesses applied by means of
pad printing are in the range of approximately 5 to 50 .mu.m of
total layer thickness.
[0017] The catalytic component which is to be applied by pad
printing contains a catalytically active material component and/or
a hydrophobic material component. The coating with the respective
material components may take place in mixed form or as individual
layers. For example, a lower layer, which contains the
catalytically active material component, can be printed onto the
plate, followed by an upper layer, which contains the hydrophobic
material component, printed onto the lower layer. Since the pad
printing can be applied not only in the form of a complete area but
also in the form of patterns, a first application of the
catalytically active material component, can be accomplished where
it is not covered completely by the subsequent printing of the
hydrophobic material component. This ensures that the reaction
gases and/or vapors can still reach the catalyst, and therefore the
catalytic activity is retained but "flooding of the catalyst", i.e.
complete coverage of the catalyst with droplets and/or a film of
liquid through condensation of water vapor, with the associated
reduction in activity or deactivation of the catalyst, is avoided.
Therefore, the combination of the catalytically active material
component with the hydrophobic material component ensures that the
reactivity of the catalyst is not impaired by the formation of
condensate at cool points of the fuel cell system, but rather is as
far as possible available in particular during a cold start. At the
same time, this combination, through adhesive bonding and/or
crosslinking, advantageously prevents the catalyst from flaking off
or being discharged or reduces these effects as far as
possible.
[0018] As has already been described in the patent application DE
10114646.9 in the name of the Applicant, which is not a prior
publication, the catalytically active material selected is
preferably metals from subgroups Ib, IIb, VIb and/or VIIb of the
periodic table; substances which are based on elements from other
groups of the periodic table, such as oxides of the rare earths,
may also be present in order to thermally stabilize the catalyst.
The at least one catalytic material component and/or
catalyst-containing material component is preferably in supported
form. There is a wide range of support materials for catalysts,
such as ceramic, carbon, plastic, and metal. Porous solids, on the
surface of which catalytically active material is deposited, are
particularly suitable. Ceramic materials, such as zeolites,
Al.sub.2O.sub.3, SiO.sub.2, ZrO.sub.2, CeO.sub.2 and/or mixtures
thereof, are particularly preferred for use as support
materials.
[0019] The at least one hydrophobic material preferably contains
silicones or silicone-containing materials, fluorinated polymers,
such as for example polytetrafluoroethylene or
polytetrafluoroethylene-containing materials, epoxy resin or epoxy
resin-containing materials, phenolic resin or phenolic
resin-containing materials, acrylic resin or acrylic
resin-containing materials, PUR adhesive materials or PUR
adhesive-containing materials or synthetic resin/shellac mixtures
or synthetic resin-containing/shellac-containing mixtures. In the
field of the fluorinated polymers, polytetrafluoroethylene (PTFE)
is a particularly suitable hydrophobic component and binder for
catalysts. With regard to the silicones, it is particularly
preferred to use silicone resins, which must have a high long-term
thermal stability in the range of use. These use temperatures lie
in the range between approximately 30.degree. C. to 650.degree. C.,
preferably in the range between approximately 50.degree. C. to
300.degree. C. A further advantage comes from the fact that, when
precious metal is used as the catalytically active material
component in combination with silicones as the hydrophobic material
component, there are no poisoning phenomena caused by catalyst
poisons, as is the case, for example, when copper is used as
catalytic component.
[0020] Moreover, it is extremely advantageous if the layer which
contains the hydrophobic material component has an elasticity which
results from the chemical substance itself and additionally
prevents flaking or discharge of the catalyst from the layer or
substantially reduces these effects. The crosslinking of the
hydrophobic material component leads to the latter acting as a
binder for the catalyst. The proportion of hydrophobic material
component in relation to the catalytically active material
component and/or catalyst-containing material component is 1 to 50%
by weight, preferably 5 to 25% by weight.
[0021] The catalyst paste or suspension or liquid which is required
for printing may preferably include, in addition to at least one
catalytically active material component, a ceramic binder, which
can also be crosslinked after calcining in air at approximately
500.degree. C., and water. Oxides and/or hydroxides of Al, Ce, Si,
Zr and/or mixtures thereof, are suitable ceramic binders; it is
preferable to use those which can be crosslinked.
[0022] If the catalyst paste or suspension or liquid which is
required for printing contains a polymeric binder which decomposes
at the temperatures required for calcining, the calcining step is
eliminated and all that follows is one or more drying steps. One
exception to this is the use of PTFE as polymeric binder, since
this material is able to withstand relatively high temperatures for
a short time.
[0023] Further additives, for example for controlling the
viscosity, the wetting behavior on the stamp or to set the pH, may
also be present in the printing paste, suspension or liquid. To
achieve an optimum printed image, the shape of the stamp must be
matched to the area which is to be printed. The matching of the
process parameters to the printing operation are dependent on the
material, temperature and process step and can be achieved by means
of standard specialist printing knowledge.
[0024] The printing operation itself is preferably carried out at
room temperature, without the printing medium (the stamp or pad) or
the coating material (printing paste, suspension or liquid) being
heated.
[0025] During the application of the catalytic component, the heat
exchanger plate can be heated to up to 200.degree. C. This
advantageously results in more rapid drying of the coating
material, particularly during multiple printing.
[0026] If the heat exchanger plate is not heated when the printing
paste, suspension or liquid is being applied to it, the printing
step is followed by a drying step in a temperature range from
approximately 100.degree. C. to 200.degree. C. in order to improve
adhesion of the coating. Circulating-air/continuous dryers, but
also radiation dryers, for example those using infrared, can be
used for drying. The drying time required is governed by the rate
of passage of the plate or plate strip. Further printing operations
may follow the drying step.
[0027] Then, the calcining step which concludes the process is
carried out at approximately 500.degree. C., contributing to final
drying and to crosslinking of the ceramic binder contained in the
coating. The duration of the calcining step is between 0.5 and 4
hours.
[0028] If, for example, silicone or silicone-containing material,
which decomposes at the temperatures required for calcining, is
used as hydrophobic material component, the calcining step has to
take place before the application of the silicone or
silicone-containing material. To dry the silicone or
silicone-containing layer which is subsequently applied, one or
more drying steps are subsequently carried out.
[0029] The heat exchanger plates which are produced using the
process according to the invention are equally suitable for use as
reactor in hydrogen, reformate and direct methanol fuel cell
systems.
[0030] The foregoing disclosure has been set forth merely to
illustrate the invention and is not intended to be limiting. Since
modifications of the disclosed embodiments incorporating the spirit
and substance of the invention may occur to persons skilled in the
art, the invention should be construed to include everything within
the scope of the appended claims and equivalents thereof.
* * * * *